Photographic emulsion



Patented F eb. 23, 1932 UNITED STATES PATENT I OFFICE LESLIE GEORGE SCOTT BROOK-ER, OF ROCHESTER, NEW YORK, ASSIGNOR 'IO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK PHOTOGRAPHIO EMULSION No Drawing.

This invention relates to a new composition of matter, and particularly to a new class of photographic sensitizing dyes, and a method for their preparation, and emulsions containing them. i

As ordinary photographic emulsions are generally indifferent to those colors of the spectrum of longer Wave lengths, various types of sensitizing dyes have been suggested for incorporation in photographic emulsions, or for employing over emulsions as overcoatings so as to increase the spectral sensitiveness thereof. Man cyanine dyes have been described for this purpose con 'taining the benzothiazole nucleus, whilst classes of these photo-sensitizing dyes con taining the naphthothiazole nucleus are described in my co-pending applications of Serial Nos. 33? 17'? filed February 2, 1929; 435,- ltll and 435,105, filed March 12, 1930; and rlil'gOli", tiled ll larchilll 1930 whilst those containing the thiazoline nucleus are described in my co-pending application Serial No. M29548 filed June 11, 1930, and those containing the thiazolenucleus, are described in my (to-pending application Ser. No. 548,- 0126, filed June 30, 1931.

An object or the present invention is to provide a process for the preparation ofphoto-sensitizing dyes of the thiocarbocyanine series contalmng benzothiazole nuclei Application filed December 31, 1930. Serial No. 505,982.

added to photographic emulsions or coated thereon as an overcoating whereby the spectral sensitivity of the photographic emulsion is increased. Other objects will hereinafter appear, such as to provide a photographic emulsion which contains or in which is incorporated or which has been treated with the herein described photo-sensitizing dyes. This silver halide emulsion may be of the gelatino silver halide type or, in fact, any type of photographic emulsion customaril employed in the art.

I ave found that dyeshaving good photosensitizing properties ma be prepared by the treatment of a 1-methy benzothiazolealkyl quaternary salt with an ortho-ester of an aliphatic carboxylic acid, the acid correspond ing to which contains more than two carbon atoms in the molecule. The reaction may be carried out in boiling dry vpyridine. Urthoesters. of the carboxylic acids which have been found particularly suitable include such esters as trirnethyl ortho-propionate, methyldiethyl ortho-n-caproate, methyldiethyl ortho-iso-caproate, and trimethyl orthovalerate.

The reaction of a Lmethylbenzothia alkyl quaternary salt with one of these 01-a mesters ofa carboxylic acid in the presence of pyridine may be written graphically as follows:

and having alkyl substituents with more than one carbon atom in the radical attached to the central carbon atom of the three-carbon chain.

A further object of this invention is to provide such photo-sensitizing dyes as may be In the above structures R represents an alkyl group and X an acid radical. A stands for the alkyl group to be introduced into the three-carbon chain of the thiocarbooyanine dye and. OR and OR represent the alkoxy groupings of the ortho-ester and these may be similar or dissimilar. The dye molecule is numbered as shown, so that a compound of this type may be described as a 2 2'-dialkyl- 8-alkyl-thiocarbocyanine salt.

In the actual practice it is frequently desirable to carry out the condensation with an acid radical such as the p-toluenesulfonate, which confers a comparatively high degree of solubility on the l-methylbenzothiazole alkyl quaternary salt and on the dye. The latter is then conveniently isolated as a less soluble salt by double-decomposition in the ordinary way, such salts as ammonium or potassium bromide or iodide being employed for this purpose, usually in aqueous solution.

The CH= group is called the methenyl group and therefore the chain -cH=cHoH may be called a tri-methenyl chain, and the chain may similarly be called a tri-methenyl chain in which the hydrogen attached to the, central carbon atoms has been replaced by the group denoted by the letter A.

The nomenclature and numbering of the above classes of compounds and intermediates are in accord with present usage and also the system used in my co-pending applications given above. The numbering, of course, is arbitrary and is given for the guidance of those skilled in the art in order that there be no question as to the identity of a compound covered by my invention.

The methods for the formation of the 1- methylbenzothiazoles (used in the preparation of the photographic sensitizing dyes.

herein described) are given in the literature. One general method consists of the conversion of the acetyl compound of an aromatic primary amine, such as p-t0luidine,- into the thio-aeetyl compound by the action of phosphorous pentasulfide. This thio-acetyl compound is then dissolved in aqueous caustic alkali solution and oxidized with a cold aqueous solution of alkali ferricyanide whereupon the base is produced and may be extracted with ether.

The preparation of some of the ortho-esters of the aliphatic earboxylicacids, the acids corresponding to which have more than two carbon atoms in the molecule have not, however, been described in'thc literature and I will give here, therefore, one method for their preparation. These ortho-esters are prepared by taking the nitrile'of the corresponding acid as the starting material. The nitri-le (one mol.) is dissolved in dry absolute ethyl ether together with an alcohol (1 mol.) such as methyl or ethyl alcohol, all of the reactants being as free from moisture as possible, and dry hydrochloric acid gas (rather more than 1 mol.) is led in, using good cooling throughout the operation. The .imino-ether hydrochloride separates and the whole is kept cold until crystallizationrappears to be complete, when the or less completely and the formation of the ortho-ester is accompanied by the separation of ammonium chloride, the formation of. which may be used as an indication of the course of the reaction.

The reaction vessel is tightly stoppered and allowedto stand for several days or even several weeks until the reaction is apparently complete. The insoluble material is then filtered off and the excess alcohol is removed by distillation, filtering again if necessary. The ester is finally distilled over, using diminished pressure as a rule, and is purified by refraetionation. Thus propionitrile on treatment with methyl alcohol and hydrochloric acid gas in the manner described above yields propio-imino-methyl-ether hydrochloride, and this, when subjected to the action of methyl alcohol in the manner described, yields trimethyl ortho-propionate. Mixed esters may be made by taking two different alcohols for the two separate steps of the reaction. Thus n-capronitrile may be converted into n-capro-imino-metl1yl-eth-er hydrochloride by the joint action of methyl alcohol and hydrochloric acid gas and this on further treatment with ethyl alcohol yields methyldiethyl ortho-n-caproate as the principal product. The ortho-esters of other aliphatic carboxylic acids having more than two carbon atoms in the molecule may be prepared in a similar manner.

I will now give several examples for preparing various dyes referred to, but it will be understood that they are merely representative of a great number of reactions in III which the proportions given and equivalents,

used may vary in accord with the particular type of dye required. My invention, therefore, will not be restricted thereby except as indicated in the appended claims.

The l-methylbenzothiazolc used in any of Example 1: 2 tricthylzfhz'ocarboq m nine iodide I 6.1 g. (1 mol.) of l-methylbenzothiazole till ethiodide was refluxed for one hour with 5.4; g. (2 mols, 300% excess) trimethyl,ortho-- stand for several days to crystallize out.

Greenish-bronze crystals were obtained, weighing 0.6 g., which were crystallized from a mixture of acetone and methyl alcohol. .Dark green prisms separated showing. a bronze reflex and the solution was bluish-red.

Er larger yield of the material was obtained as follows: 7 g. (1 mol.) of l-methylbenzothiazole etho-p-toluene-sulfonate was boiled under reflux for one hour with 2.7 g. (1 mol.) triinethyl ortho-propionate and 7 cc. dry pyridine. A warm solution of 10 g. potassium iodide in 50 cc. water was added and the iodide of the dye was filtered off when cold and obtained as a dull greenish-black powder weighing 3.67 g. after washing with water and with cold acetone. This was crystallized from 50 cc. methyl alcohol using an extraction apparatus and on cooling the dye crystallized out in beautiful prisms, some faces of which reflected blue light and others green light.

it in place or the l-methylbenzothiazole ethop-toluene-sulfonate used above, one employs 6.? g. (1 mol.) of l-methylbenzo'thiarole nietho-p-toluenesulfonate (made by condensing equiinolecular proportions of 1-rnethylbenzothiazole and methyl-p-toluenesulinnate together overnight on the steam bath and crystallizing the crude salt from methyl alcohol and drying it well) and refluxes it lor an hour with 2.7 g. (1 mol.) of trimethyl ortho-propionate and cc. pyridine, 2'- dimethyl-B-ethylthiocarbocyanine p-toluenesull onate will be produced. The dye may be isolated as the bromide by precipitating it with an excess or an aqueous solution of am inonirun bromide and weighed 2.9 g. when dry. The dye crystallizes from methyl alcohol in purplish-brown needles with a green reflex, and gives a bluish-red solution in this solvent.

Example 93.8 ethyt' 2 2 diaZZy Zthiooarhw og aniae iodide 12.? g. (1 mol.) of 1-methylbenzothiazole alliodide (made by condensing the base with an equivalent amount of allyl iodide and purifying the product byrecrystallizing it) was refluxed for forty-five minutes with 10.8 g. (:2 mole.) trimethyl ortho-propionate and 40 cc. of pyridine. A solution of 10 g. of potassiurniodide in 200 cc. of water was added and the mixture cooled in ice Water and stirred with ether to induce crystallization. The dye was filtered off, washed alternately with water and with acetone and dried. A dull purplishdarown powder weighing 1.67 g. was obtained. The dye was obtained (tree from a less soluble by-product) as dark greenish crystals with a pale bronze reflex.-

Eazample 51-5.- 5'-dimeth Z-!Z.- i a-mezh zthiooarbocyanine iodide ing. The dye was crystallized from methyl alcohol, dark green crystals being obtained which gave a bluish-red solution in this solvent.

EwampZe 4.-2 2 dimethyl 8 nbuti Zthiooarbocg anine iodide E trample 5 .22 92.-diethy/Ldmbutyltiiiocarbocyanine iodide 7 .0 g. (1 mol.) l-lnethylbenzothiazole ethop-toluene-sulfonate was refluxed with 6.5 g. (2 mols.) of trimethyl'ortho-n-valerate and 20 cc. dry pyridine for forty minutes. The dye was precipitatcdas the iodide using a solution of 20 g. potassium iodide in 100 cc. hot water, when rapid crystallization occurred. The dye weighed 3.8 g. after filtering, washing and drying, and when recrystallized from methyl alcohol formed beautiful greenish-gray crystals with a marcasite-like lustre, which gave a bluish-red solution in the solvent.

E'zvample 6.2 2dime/itg l-8-n-amylthiooarbooyanine iodide 6.7 g. (1 mol.) l-methylbenz othiazole metho-p-toluene-sulfonate was refluxed for drying. When recrystallized from diethyl ortho-n-eaproate (obtained from ncapronitrile) and 30 cc..dry pyridine. The dye was then precipitated as the iodide using a solution of 10 potassium iodide in 50 cc. hot water for t is purpose. The product an hour with 8.2 g. (2 mole.) of inethyl- .125.

crystallized on coolin and was filtered off, washed, and dried. eight 3.4 g. Reddish needles with a brilliant blue reflex were obtained on recrystallizing the dye from methyl alcohol, the solution being bluish-red.

Ewample 7.2 W-dz'ethyZ-8 -namylthiocarbocyanines iodide red solution.

Emamp le 8.-2 2 dimethyl 8 z'soamylthiocarbocyam'ne iodide 6.7 (1 mol.) l-methylbenzothiazole metho-p-toluene-sulfonate was refluxed with 8.2 g. (2 mols.) methyldiethyl ortho-isocaproate (obtained from isocapronitrile) and 20 cc. pyridine for forty minutes. The dye was precipitated as the iodide, using a solution of 10g. potassium iodide in 50 cc. of hot water, and weighed 1.8 g. when filtered off, washed, and dried. It crystallized from methyl alcohol in compact dark bluish-grey prisms with a green reflex, and gave a blulshred solution in this solvent.

By substituting various alkyl groups having more than one carbon atom in the position in the structural formula of the dye occupied by the letter fi, and various alkyl groups in the two positions occupied by the letter R, many sensitizing dyes may be obtained. The letter X indicates any suitable anion such,. for example, as a halide, p-toluenesulfonate, alkylosulphate, nitrate, acetate, perchlorate, or, in fact, any salt forming anion that will not render the dye too sparingly soluble or dele'ter'iously affect the photographic sensitizing properties of the d 'e.

In the preparation of emulsions containing these photographic sensitizers, it has been found that the dye may be dissolved in methyl alcohol and a volume of solution containing from 5 to 100 milligrams ofdye added to 1000 cc. of emulsion. While it may not be necessary to add some of the sensitizers in a large amount, it may be necessary to add others in amounts larger than those given above; generally about to milligrams is sufiicient to obtain the maximum sensitizing efiect with a dye having good sensitizing power. The more powerful dyes, however, may require much less. The regulation or adoption of the most economical proportions will be apparentto those skilled in the art upon observing the sensitizing power of the particular dye for the particular emulsion to be formed. The above examples are, therefore, illustrative and not to be understood as limiting the invention in any sense, as it will be apparent that these dyes may be incorporated by other methods in many of the photographic emulsions customarily employed in the art, such for instance as by bathing the plate or film, upon which the emulsion has been coated, in a solution of the dye in an appropriate solvent although this method of incorporating the dye in the emulsion is not preferred over that above described. Obviously the claims are all intended to cover any combination of these dyes with a photographic emulsion whereby the dye exerts a sensitizing effect upon the emulsion.

It is apparent from a-thorough consideration of the above description that any thiocarbocyanine dye prepared from a l-methylbenzothiazole unsubstituted or substituted, in

' which the 8 position of the dye is substituted by an alkyl group containing more than one carbon atom, will come within the scope of this invention whatever may be the radicals occupying the other substitutable positions of the structure, together with the employment of such dyes for photographic sensitizing and other purposes. Furthermore, it will also be apparent that the genus claimed hereinafter not only includes the foregoing but also includes any carbocyanine dye containing two of the five-membered rings.

linked together by a tri-methenyl chain, the hydrogen attached to the central carbon atom of which is substituted by an alkyl group containing more than one carbon atom such as, for example, the S-substituted thiocarbocyanines derived from mu-methylnaphthothiazole described in my application Serial No. 435,104, the 7 -substituted thiazolinocarbocyanines derived from 2-methylthiazoline described in my application Serial No. 460,548 and the 7-substituted thiazolocarbocyanines derived from Q-methylthiazole described in my application Ser. No. 548,026.

In the claims, by an ortho-ester of an aliphatic carboxylic acid is meant an ortho-ester of a carboxylic acid, the acid corresponding to which. contains a simple, unsubstituted alkyl group directly attached to the carbon atom of the carboxyl group. Examples of such ortho-esters have already been given.

What I claimas my invention and desire to be secured by E'etters Patent of the United States is:

1. A photographic gelatino-silver-halide emulsion which contains a carbocyanine dye 1 comprising two heterocyclic rings of the structure with onemolecular proportion of an orthoester of a monobasic aliphatic carboxylic acid having more than two carbon atoms.

3. A photographic gelatino silver halide emulsion which contains a thiocarbocyanine dye substituted in the 8 position with an alkyl radical containing more than one carbon atom.

4. A photographic gelatino silver halide emulsion which contains a. thiocarbocyanine dye substituted in the 8 position with an alkyl radical containing more than one carbon atom, said .dye containing two benzothiazole nuclei.

5. A photographic gelatino silver halide emulsion which contains a 2:2-dialkyl-8-allrylthiocarbocyanine salt in which the 8-alkyl group contains more than one carbon atom.

6. A photographic gelatino silver halide emulsion which contains a 2:2-dialykl-8- allrylthiocarbocyanine salt in which the 8- aklyl group contains more than one carbon atom, said salt containing two benzothiazole nuclei.

7. A photographic gelatino silver halide emulsion which contains a thiocarbocyanine dye resulting from the condensation of two molecules of a l-methylbenzothiazole alkyl quaternary salt with an ortho-cster of a monobasic aliphatic carboxylic acid having more than two carbon atoms.

8. A photographic gelatino silver halide emulsion which contains a 5:5'-dimethyl- 2 2'-8-triethylthiocarbocyanine salt. 4

9. A photographic gelatino silver halide emulsion which contains a 2:2-diniethyl-8- n-butylthiocarbocyanine salt.

10. A photographic gelatino silver halide emulsion which contains a 2:2-dimethyl-8- ethyl-thiocarbocvanine salt.

11. Aphotographic gelatino silver halide emulsion which contains a 2:2-dialkyl-'8- alkylthiocarbocyanine halide in which the 8 alkyl group contains more than one carbon atom.

12. A photographic gelatino silver halide emulsion which contains 5: 5'-dimethy1- 2 2'-8-triethylthiocarbocyanine iodide.

13. A photographic gelatino silver halide emulsion which contains 2:9"-dimethyl-8-nbutylthiocarbocyanine iodide.

14. A photographic gelatino silver halide emulsion which contains 2:2-dim ethyl-8- ethyl-thiocarbocyanine bromide.

15. As an article of manufacture, a supporting surface coated with a photographic gclatino-silver-halide emulsion including. a 2 2-dialkyl-8-alkylthiocarbocyanine salt in which the 8-alkyl group contains more than one carbon atom.

Signed at Rochester, N. Y., this 29th day of December, 1930.

LESLIE GEORGE SCOTT BROOKER. 

